Fluids at high pressure are used for various purposes. High pressure fluids are often used in high pressure streams in fluid blast systems for cleaning purposes. Such high pressure streams are, for example, used for cleaning surfaces, for cleaning unwanted coatings or deposits off surfaces particularly metal and concrete surfaces, and for cleaning the interior surfaces of vessels and tubes particularly to remove scale and other deposits.
High pressure fluid streams are generally controlled by meanas of a fluid control apparatus which includes a high pressure discharge outlet for discharging a high pressure fluid stream, a pressure relief low pressure dump outlet for relieving pressure when discharge of the high pressure fluid stream is to be discontinued, and a control valve arrangement for controlling flow between the high pressure discharge outlet and the low pressure or dump outlet.
High pressure fluid streams are often provided at pressure of between about 5,000 and about 20,000 p.s.i.a., and typically at about 10,000 p.s.i.a. for cleaning purposes. At these pressures the streams can be extremely hazardous.
To reduce the potential hazard of such streams, the fluid control apparatus is usually designed so that pressure flow through the high pressure discharge outlet can only continue while an actuating member is held in its operative position to thereby hold a valve closure member in its seated condition. As soon as the actuating member is released, the valve closure member will be unseated and the pressure will be relieved through the dump outlet for the high pressure fluid stream to drop to a low pressure.
Since these fluid control devices are usually mobile, hand held and manually actuated, it is highly desirable for the devices to require a small operating force to hold the valve member in its seated or closed position. However, because of the high pressures involved, a relatively large force is typically required to hold the valve member on its seat in order to prevent release of pressure through the dump outlet.
To overcome this high valve closure member seating force, rather complicated and costly actuating apparatus has been devised. Examples of these are the cam-assisted valve member actuator described in U.S. Pat. No. 3,672,575, Hinrichs, and the power-assisted and pilot-valve assisted apparatus described in U.S. Pat. No. 4,349,154.
Leakage through the dump outlet results in losing fluid pressure and flow in the high pressure system, and such leakage also usually allows the high pressure fluid to quickly erode the valve seat surface. The resulting seat damage requires that the fluid control apparatus be removed from service frequently and repaired. It is therefore highly desirable in this type device that a low, manageable valve member closing force be maintained.
The factors that generally determine the magnitude of the valve member closing force in this type of apparatus are the hydraulic areas on which the high pressure fluid acts in the closed or seated position of the valve element, and the axial alignment between the sliding valve member and its stationary seat.
Attempts have been made to reduce the effects of the valve member hydraulic areas through the use of a pilot valve that works in conjunction with a main valve member. However, a pilot valve introduces an additional high pressure seat into the apparatus, and results in a more complex assembly, higher manufacturing costs, and generally greater field maintenance requirements for the apparatus.
Other attempts to overcome the effects of the valve member hydraulic areas have been to utilize a single element valve closure member with various special seating configurations. However, these constructions fail to take into consideration the hydraulic effects that variances in the closure member's trailing end high pressure seal can have on the closure member forces. Such single element structures also have been prone to wide variations in hydraulic forces due to sealing area wear during use.
The axial alignment between the sliding valve element and its seat is considered to be quite critical to the magnitude of the operating force that is required to keep the valve element in its closed or seated position. This is because a very precise coaxial mating condition is required to provide an effective metal-to-metal seal between the valve element and seat, particularly in the presence of high fluid pressures. In the fluid control apparatus now being used, the alignment between the sliding valve member and its seat is very difficult to maintain because each of these members operate with diametral clearance within separate bores in the valve body. The diametral clearance between the valve member and its bore, and between the seat and its bore, allows each member to become laterally displaced with respect to each other during operation. Because the seating surfaces on the valve member and its seat have corresponding tapers, the lateral displacement condition can usually be overcome with additional closing force on the valve member. However, the requirement for use of additional closing force is contrary to the desirable low operating force level from the actuating means.
Any surface wear on the sliding valve member and its guiding bore in the body will allow even more lateral displacement or misalignment with respect to the seat, and an even greater closing force is required from the actuating means. When wear occurs, replacement of the valve member alone may not solve the problem. The new valve closure member will again be subject to misalignment. Only by replacing both the expensive valve body and the valve member will the valve member and seat alignment be restored to a like-new condition. This is not only costly but time consuming.
Still another problem encountered with these fluid control devices is that they require frequent field maintenance. In addition to surface wear on the valve closure member and its seal due to frequent opening and closing, damage to the precision seat surface frequently occurs when small grains of hard foreign matter such as rust or sand particles scratch the seat surface while being entrained in the high velocity flow stream that is produced across the seating surface at the instant when the closure member moves away from the seat to release the fluid pressure in the system. Once the seat surface is damaged, fluid erosion due to high pressure fluid leakage quickly enlarges the seat damage, the replacement of the closure member and its seat becomes necessary. Such repair is time consuming and usually requires a higher degree of skill than that possessed by the average control device operator.
It is accordingly a general object of the present invention to provide a new and improved fluid control device which is constructed and arranged to overcome or at least partly reduce the foregoing disadvantages with prior devices.
Another object of the present invention is to provide a new and improved hand-held or foot controlled fluid blast apparatus which requires a very low actuating force in operation.
Still another object of the present invention is to provide a new and improved fluid blast control apparatus that is easier, faster and less expensive to repair and overhaul in the field.